When NASA's Mars Exploration Rover Opportunity left Victoria Crater two years ago this month, the rover science team chose Endeavour Crater as the rover's next long-term destination. With a drive of 111 meters (364 feet) on Monday, Sept. 6, Opportunity reached the estimated halfway point of the approximately 19-kilometer (11.8-mile) journey from Victoria to the western rim of Endeavour.

Opportunity completed its three-month prime mission on Mars in April 2004. During its bonus extended operations since then, it spent two years exploring in and around Victoria Crater. Victoria is about 800 meters (half a mile) in diameter. At about 22 kilometers (14 miles) in diameter, Endeavour is about 28 times wider. After the rover science team selected Endeavour as a long-term destination, observations of Endeavour's rim by NASA's Mars Reconnaissance Orbiter revealed the presence of clay minerals. This finding makes the site an even more compelling science destination. Clay minerals, which form exclusively under wet conditions, have been found extensively on Mars from orbit, but have not been examined on the surface.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington. For more about the twin rovers Spirit and Opportunity, see http://marsrovers.jpl.nasa.gov/home/index.html.